Campbell CNR4 User manual

CNR4 Net Radiometer
Revision: 11/10
Copyright © 2000-2010
Campbell Scientific, Inc.

Warranty and Assistance
The CNR4 NET RADIOMETER is warranted by Campbell Scientific, Inc. to
be free from defects in materials and workmanship under normal use and
service for twelve (12) months from date of shipment unless specified
otherwise. Batteries have no warranty. Campbell Scientific, Inc.'s obligation
under this warranty is limited to repairing or replacing (at Campbell Scientific,
Inc.'s option) defective products. The customer shall assume all costs of
removing, reinstalling, and shipping defective products to Campbell Scientific,
Inc. Campbell Scientific, Inc. will return such products by surface carrier
prepaid. This warranty shall not apply to any Campbell Scientific, Inc.
products which have been subjected to modification, misuse, neglect, accidents
of nature, or shipping damage. This warranty is in lieu of all other warranties,
expressed or implied, including warranties of merchantability or fitness for a
particular purpose. Campbell Scientific, Inc. is not liable for special, indirect,
incidental, or consequential damages.
Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
serves your country.
To obtain a Returned Materials Authorization (RMA), contact Campbell
Scientific, Inc., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container. Campbell
Scientific's shipping address is:
CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
For all returns, the customer must fill out a “Declaration of Hazardous Material
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
435-750-9579. Campbell Scientific will not process any returns until we
receive this form. If the form is not received within three days of product
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CNR4 Table of Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. General Description.....................................................1
2. Sensor Specifications .................................................2
2.1 CNR4 Specifications ................................................................................3
2.2 Pyranometer Specifications ......................................................................4
2.3 Pyrgeometer Specifications ......................................................................5
2.4 Optional CNF4 Heater/Ventilator.............................................................5
2.4.1 CNF4 Specifications .......................................................................6
3. Installation....................................................................6
4. Using the Optional CNF4 Heater/Ventilator Unit.......8
5. Using the CNR4 in the Four Separate Components
Mode ...........................................................................9
5.1 Measuring Short-wave Solar Radiation with Pyranometer ......................9
5.2 Measuring Long-wave Far Infrared Radiation with Pyrgeometer............9
5.3 Measuring CNR4 Temperature with Thermistor....................................10
5.4 Calculation of Albedo.............................................................................12
5.5 Calculation of Net Short-wave Radiation...............................................13
5.6 Calculation of Net Long-wave Radiation ...............................................13
5.7 Calculation of Net (Total) Radiation ......................................................14
6. Wiring..........................................................................14
7. Datalogger Programming..........................................17
7.1 Sensor Sensitivity ...................................................................................17
7.2 Example Programs..................................................................................17
7.2.1 Example 1, CR1000 Program Using Differential Measurements .17
7.2.2 Example 2, CR3000 Program Using Differential Measurements .21
7.2.3 Example 3, CR5000 Program Using Differential Measurements .24
8. Troubleshooting ........................................................28
8.1 Testing the Pyranometer .........................................................................28
8.2 Testing the Pyrgeometer .........................................................................29
8.3 Testing the Thermistor............................................................................29
8.4 Testing the Pt-100...................................................................................29
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CNR4 Table of Contents
9. Maintenance and Recalibration ................................29
9.1 Cleaning Windows and Domes.............................................................. 29
9.2 Recalibration .......................................................................................... 30
9.3 Replacing the Drying Cartridge ............................................................. 30
9.4 Replacement Parts.................................................................................. 31
Appendices
A. CNR4 Performance and Measurements under
Different Conditions ............................................. A-1
B. CNF4 Heater/Ventilator ........................................... B-1
B.1 General Information ............................................................................ B-1
B.2 Attaching the Optional CNF4 Heater/Ventilator Unit to CNR4 ......... B-3
B.3 Wiring ................................................................................................. B-7
B.4 Example B, CR3000 Datalogger Program with Heater/Ventilator
Control............................................................................................. B-8
B.5 CNF4 Heater/Ventilator Maintenance............................................... B-11
B.5.1 Testing the Heater.................................................................... B-11
B.5.2 Testing the Ventilator .............................................................. B-11
B.5.3 Replacing the Filter for the Ventilator..................................... B-12
C. CR3000 Program for Measuring Pt-100
Temperature Sensor.............................................C-1
Figures
2-1. The CNR4 net radiometer with cables and mounting rod, top view ...... 2
2-2. The CNR4 net radiometer with CNF 4 heater/ventilator unit, top view. 2
3-1. Attaching the mounting rod to the CNR4 body...................................... 7
3-2. Attaching the CNR4 onto the mounting rod (CSI p/n 26120) using
vertical pole or horizontal crossarm .................................................... 8
6-1. The CNR4 sensor with SOLAR and TEMP cables .............................. 14
6-2. The marks on the end of the CNR4: S for SOLAR cable, and T for
TEMP cable....................................................................................... 15
6-3. Labels on the pigtail end of the SOLAR cable ..................................... 15
6-4. Labels on the pigtail end of the TEMP cable........................................ 16
9-1. Replacing the Drying Cartridge............................................................ 30
A-1. Different measurement conditions and signals .................................. A-2
A-2. Partly cloudy day for the upward facing pyrgeometer....................... A-2
A-3. Clear day for the downward facing pyrgeometer .............................. A-3
B-1. CNF4 Package Contents .................................................................... B-3
B-2. Attaching the CNF4 to CNR4 using pan-head screws and washers .. B-4
B-3. Making sure the cables are clear from the edges ............................... B-5
B-4. CNF4 solar shield and four flat-head screws ..................................... B-5
B-5. Attaching the solar shield to CNF4 using four flat-head screws........ B-6
B-6. Affixing the sensor label to CNF4 ..................................................... B-6
B-7. Connecting the CNF4 power control cable and the mounting rod..... B-6
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CNR4 Table of Contents
Tables
5-1. Resistance values versus CNR4's thermistor temperature in °C ...........11
5-2. Resistance values versus CNR4's Pt-100 temperature in °C .................12
6-1. Datalogger Connections for Differential Measurement ........................16
6-2. Datalogger Connections for Single-ended Measurement......................16
A-1. Typical output signals of CNR4 under different meteorological
conditions. Explanation can be found in the text ........................... A-1
B-1. CR1000 and CR3000 Datalogger Connections for Differential
Measurement with Heater/Ventilator Control..................................B-7
C-1. Datalogger Connections for Differential Measurement with Pt-100 ..C-1
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CNR4 Table of Contents
iv

CNR4 Net Radiometer
1. General Description
The CNR4 is a four component net radiometer that measures the energy
balance between incoming and outgoing radiation.
The CNR4 net radiometer consists of a pyranometer pair, one facing upward,
the other facing downward, and a pyrgeometer pair in a similar configuration.
The pyranometer pair measures short-wave solar radiation, and the
pyrgeometer pair measures long-wave far infrared radiation. The upper long-
wave detector of CNR4 has a meniscus dome. This ensures that water droplets
roll off easily and improves the field of view to nearly 180°, compared with a
150° for a flat window. All four sensors are integrated directly into the
instrument body, instead of separate modules mounted onto the housing. Each
sensor is calibrated individually for optimal accuracy.
Two temperature sensors, a thermistor and a Pt-100, are integrated with the
CNR4 body. The temperature sensor is used to provide information to correct
the infrared readings for the temperature of the instrument housing. Care has
been taken to place the long-wave sensors close to each other and close to the
temperature sensors. This assures that the temperatures of the measurement
surfaces are the same and accurately known. This improves the quality of the
long-wave measurements. Campbell Scientific adds a completion resistor in
the pig tail end of the thermistor cable, so that it is easily interfaced with our
dataloggers for half-bridge measurement.
The CNR4 design is very light in weight and has an integrated solar shield that
reduces thermal effects on both the short-wave and the long-wave
measurements. The cables are made from Santoprene®jacket, which is
intended for outdoor use, and is resistant to a variety of pollutants and UV-
radiation. The mounting rod can be unscrewed for transport.
An optional ventilation unit with a heater, CNF4, is designed as an extension of
the solar shield and can be fitted new to the CNR4 or retrofitted later. The
heater/ventilation unit is compact and provides efficient air-flow over the
domes and windows to minimize the formation of dew and to reduce the
frequency of cleaning. The integrated heater can be used to melt frost.
The CNR4 specifications when used with CNF4 comply with the WMO
classification of Good Quality.
The CNR4 design is such that both the upward facing and the downward-
facing instruments measure the energy that is received from the whole
hemisphere (180° field of view). The output is expressed in W/m2. The total
spectral range that is measured is roughly from 0.3 to 42 μm. This spectral
range covers both the short-wave solar radiation, 0.3 to 2.8 μm, and the long-
wave far infrared radiation, 4.5 to 42 μm. The gap between these two produces
negligible errors.
Unlike the CNR1, four probes in the CNR4 have different sensitivity values.
This makes each measurement from four sensors more accurate than when they
are made to have the same sensitivity value with shunt and series resistors.
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CNR4 Net Radiometer
2. Sensor Specifications
The CNR4 consists of two pyranometers, for measuring short-wave radiation,
and of two pyrgeometers for measuring long-wave radiation. Two temperature
sensors are available as standard, a thermistor and a Pt-100. The optional
heater/ventilator unit CNF4-L is available. See Appendix B for more
information on the CNF4-L.
The properties of the CNR4 are mainly determined by the properties of the
individual probes. Generally the accuracy of the CNR4 will be higher than that
of competitive net-radiometers, because the solar radiation measurement
performed by the pyranometer is accurate, and offers a traceable calibration.
Also the optionally integrated heater/ventilator unit improves the accuracy.
Due to the fact that the net short-wave radiation can be very intense, 1000
W/m2compared to a typical -100 W/m2net long-wave radiation, the accuracy
of the short-wave radiation measurement is critical. Wind corrections, as
applied by less accurate competitive instruments are not necessary. The robust
materials used imply that the CNR4 will not suffer damages inflicted by birds.
Figure 2-1 and Figure 2-2 show the CNR4 with and without the CNF4
heater/ventilator. From a spectral point of view, the pyranometer and
pyrgeometer are complementary, and together they cover the full spectral
range.
FIGURE 2-1. The CNR4 net radiometer with cables and mounting rod, top view.
FIGURE 2-2. The CNR4 net radiometer with CNF 4 heater/ventilator unit, top view.
2

CNR4 Net Radiometer
2.1 CNR4 Specifications
Sensor sensitivities: Four probes have unique sensitivity
values. Please refer to the calibration
sheets or label on the bottom of the
sensor for the sensitivity values.
Operating temperature: -40 to +80°C (-40 to 176°F)
Operating humidity: 0 to 100 % RH
Bubble level sensitivity: < 0.5°
Sensor type: Thermopile
Receiver paint: Carbon Black
Desiccant: Silica gel (replaceable)
Housing material: Anodized aluminum body
Shock/vibration: IEC 721-3-2-2m2
CE: Complies with EC guideline
89/336/EEC 73/23/EEC
Environmental protection: IP 67
Requirements for data acquisition
Radiation components: 4 differential or 4 single-ended analog
channels
Thermistor: 1 voltage excitation and 1 single-
ended analog channel
Pt-100 temperature: 1 current excitation and 1 differential
analog channel.
Cable length: User defined
Weight
Sensor: 1.89 lbs (0.85 kg) without cables
Heater/Ventilator, CNF4
(optional):
1.11 lbs (0.50 kg) without cables
Mounting rod: 13.67 ” (34.7 cm) length
0.63 ” (1.6 cm) diameter
CNR4 Package includes: CNR4 sensor
Mounting rod (1 ea.)
Solar cable (labeled SOLAR)
Temperature cable (labeled TEMP)
Drying cartridges (2 ea.)
WRR Traceable Calibration
Certificate for pyranometers
WRR Traceable Calibration
Certificate for pyrgeometers
Extra Calibration Sticker (to be put on
CNF4, if used)
CNF4 Package includes: CNF4 Heater/Ventilator
CNF4 cable
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CNR4 Net Radiometer
2.2 Pyranometer Specifications
* indicates ISO specifications.
Spectral range: 305 to 2800 nm (50% points)
Sensitivity: 10 to 20 µV/W/m2
Response time*: < 18 seconds (95% response)
Non-linearity*: < 1% (0-1000 W m-2 irradiance)
Non-stability*: < 1%
Temperature dependence of
sensitivity*:
< 4% (-10° to +40°C)
Tilt response*: < 1% at any angle with 1000 W/m2
Directional error*: < 20 W/m2at angle up to 80° with
1000 W/m2
Zero offset due to 0 to -200 W/m2
IR net irradiance*:
< 15 W/m2
Zero offset due to temperature
change*:
< 3 W/m2 (5K/hr temperature change)
< 1 W/m2 (with CVF 4 installed)
Operating temperature: -40°C to +80°C
Field of view
Upper detector:
Lower detector:
180°
150° (due to lower solar shield to
prevent illumination at low zenith
angles)
Maximum solar irradiance: 2000 W/m2
Expected accuracy for daily totals: ±10 %
Typical signal output for
atmospheric application:
0 to 15 mV
Impedance: 20 to 200 Ω, typically 50Ω
Detector: Copper-constantan multi junction
thermopile
Level accuracy: 1 degree
Irradiance: 0 to 2000 W/m2
Spectral selectivity: < 3% (330-1500 nm spectral interval)
Uncertainty in daily total: < 5% (95% confidence level)
Instrument calibration: Indoors. Side by side against reference
CMP3 pyranometer according to ISO
9847:1992 annex A.3.1
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CNR4 Net Radiometer
2.3 Pyrgeometer Specifications
Spectral range: 4.5 μm to 42 μm (50% points)
Sensitivity: 5 to 15 μV/W/m2
Impedance: 20 Ωto 200 Ω(typically 50)
Response time: < 18 seconds (95% response)
Non-linearity: < 1% (-250 to +250 W/m2 irradiance)
Temperature dependence of
sensitivity:
< 4% (-10° to +40°C)
Tilt error: < 1% (deviation when tilted at any
angle off horizontal)
Zero offset due to temperature
change:
±4 W/m2 (5K/hr temperature change)
Field of view
Upper
Lower
180 degrees
150 degrees
Net-irradiance: -250 to +250 W/m2
Non-stability: < 1% (sensitivity change per year)
Window heating offset: < 6 W/m2 (1000 W/m2 solar
irradiance)
Uncertainty in daily total: < 10% (95% confidence level) indoor
calibration
Typical signal output for
atmospheric application:
±5 mV
Temperature sensors
Thermistor: 10k Ω
Pt-100: DIN class A
Instrument calibration: Indoors, side by side against reference
CG(R) 3 pyrgeometer. On request
outdoors, side by side against
reference CG(R) 4 pyrgeometer
2.4 Optional CNF4 Heater/Ventilator
The purpose of the heater/ventilator is to prevent dew deposition on the
pyrgeometer and pyrgeometer window, thus enhancing the measurement
accuracy and reliability. Using the heater/ventilator will have negligible effect
on the pyranometer reading.
Generally, the errors caused by the heater/ventilator will be small relative to the
errors that would have been caused by water deposition.
5

CNR4 Net Radiometer
2.4.1 CNF4 Specifications
Heater
Power consumption:
10 W @ 12 Vdc (15 Ω)
Ventilator
Power consumption:
Supply voltage:
5 W @ 12 Vdc
8 to 13.5 Vdc
Weight: 1.11 lbs (0.5 kg)
Operating temperature: -40 to +80°C
3. Installation
For measurement of net radiation, it is most important that the instrument is
located in a place that is representative of the entire area that one wishes to
study.
When installed on a mast, the preferred orientation should be such that no
shadow is cast on the net radiometer at any time during the day. In the
Northern Hemisphere this implies that the net radiometer should be mounted
on the south side of the mast.
It is suggested that the CNR4 is mounted at a height of at least 1.5 meters
above the surface to avoid shading effects of the instruments on the soil and to
promote spatial averaging of the measurement. If the instrument is hmeters
above the surface, 99% of the input of the lower sensors comes from a circular
area with a radius of 10h. Shadows or surface disturbances with radius < 0.1h
will affect the measurement by less than 1%.
It is recommended that the CNR4 be mounted to a separate vertical pipe at
least 25 feet from any other mounting structures. The mounting bracket (CSI
p/n 26120) is used to mount the CNR4 directly to a vertical pipe, or to a
CM20x series Sensor Crossarm. Mount the sensor as follows:
1. First, attach the mounting rod to the CNR4, as shown in Figure 3-1.
2. Attach mounting bracket (CSI p/n 26120) to the vertical mounting
pipe or CM20x series Sensor Crossarm, using the U-bolts provided
as shown in Figure 3-2.
3. Insert the mounting rod of the CNR4 sensor into a mounting block of
the mounting bracket (CSI p/n 26120), making sure the sensor points
to the direction of the arrows marked as “SENSOR” on top of the
bracket (see Figure 3-2). Perform a coarse levelling of the sensor
using the bubble level on the top of the CNR4, and tighten the four
screws on top of the mounting bracket to properly secure the
mounting rod so that it does not rotate.
6

CNR4 Net Radiometer
Do not attempt to rotate the instrument using the sensor heads, or
you may damage the sensors; use the mounting rod only.
NOTE
4. Perform the fine levelling using the two spring-loaded levelling
screws: one on the front and the other on the back of the bracket.
FIGURE 3-1. Attaching the mounting rod to the CNR4 body.
7

CNR4 Net Radiometer
FIGURE 3-2. Attaching the CNR4 onto the mounting rod
(CSI p/n 26120) using vertical pole or horizontal crossarm.
For installation in buildings or in solar energy applications, one will often have
to mount the CNR4 parallel to the surface that is being studied. This may be in
a tilted or a vertical position. The sensitivity of the radiometers will be
affected, but only in a minor way. This is specified as the so-called tilt effect.
From the specifications one can see that the tilt effect (this is a change in
sensitivity) remains within 1 % (See specifications in Section 2).
4. Using the Optional CNF4 Heater/Ventilator Unit
The optional heater/ventilator unit for CNR4 is available from the
manufacturer. You can purchase the CNF4-L heater/ventilator from Campbell
Scientific with custom cable length. Please refer to the Appendix B for details
on the CNF4 heater/ventilator, including the assembling instructions and
sample programs to control the CNF4 unit.
8

CNR4 Net Radiometer
5. Using the CNR4 in the Four Separate Components
Mode
In the four separate components mode configuration (measuring two short-
wave radiation signals, two long-wave signals), all signals are measured
separately. Calculation of net-radiation and albedo can be done on-line by the
datalogger, or off-line by the user during post-processing, using the stored raw
data.
The two pyranometers will measure the short-wave radiation, both incoming
and reflected. The two pyrgeometers will measure the long-wave radiation.
For proper analysis of the pyrgeometer measurement results, they must be
temperature corrected using the temperature measurement performed by the
onboard thermistor or Pt-100 sensor.
The following paragraphs describe how one should treat the instrument, and
how different parameters like albedo, net short-wave radiation, net long-wave
radiation, soil temperature, sky temperature, and net (total) radiation can be
calculated.
5.1 Measuring Short-wave Solar Radiation with Pyranometer
The pyranometer generates an mV signal that is simply proportional to the
incoming short-wave radiation. The conversion factor between voltage, V, and
W/m2of solar irradiance E, is the so-called calibration constant C (or
sensitivity).
For each pyranometer
E = V/C (5-1)
Measuring with a pyranometer can be done by connecting two pyranometer
wires to a datalogger. Incidental light results in a positive signal. The
pyranometer mounting plate and ambient air should be at the same
temperature, as much as possible. Conversion of the voltage to irradiance can
be done according to equation 5-1, and this is done inside the datalogger
program.
With the upward-facing pyranometer the so-called global (solar) downwelling
radiation is measured. The downward-facing pyranometer measures the
reflected upwelling solar radiation. When calculating the net radiation, the
upwelling radiation must be subtracted from the downwelling radiation. See
Section 5.5.
5.2 Measuring Long-wave Far Infrared Radiation with
Pyrgeometer
When using the pyrgeometer, you should realize that the signal that is
generated by the pyrgeometer represents the exchange of long-wave far
infrared (thermal) radiation between the pyrgeometer and the object that it is
facing. This implies that the pyrgeometer will generate a positive voltage
output, V, when it faces an object that is hotter than its own sensor housing,
and that it will give a negative voltage signal when it faces an object that is
9

CNR4 Net Radiometer
colder. This means that for estimating the far infrared radiation that is
generated by the object that is faced by the pyrgeometer, usually the sky or the
soil, you will have to take the pyrgeometer temperature, T, into account. This
is why the temperature sensors are incorporated in the CNR4's body near the
pyrgeometer sensing element, and has, therefore, the same temperature as the
pyrgeometer sensor surface. The calculation of the long-wave far infrared
irradiance, E, is done according to the following equation:
For the pyrgeometer only
E = V/C + 5.67·10-8·T4 (5-2)
In this equation C is the sensitivity of the sensor. Please bear in mind that T is
in Kelvin, and not in Celsius or Fahrenheit.
The downward-facing pyrgeometer measures the far infrared radiation that is
emitted by the ground. The upward-facing pyrgeometer measures the far
infrared radiation from the sky. As the sky is typically colder than the
instrument, one can expect negative voltage signals from the upward-facing
pyrgeometer. The Equation 5-2 is used to calculate the far infrared irradiance
of the sky and of the ground.
5.3 Measuring CNR4 Temperature with Thermistor
The CNR4 has two temperature sensors built inside: thermistor and Pt-100.
They both have the identical accuracy. We recommend using the thermistor
with Campbell Scientific dataloggers. The thermistor has a larger resistance
(10 kΩ@ 25°C) than Pt-100 sensor (100 Ω@ 0°C), and the change in
resistance with respect to temperature, in absolute terms, is greater. Therefore,
the cable resistance can be neglected, and the thermistor can easily be
measured using half-bridge measurement instruction on Campbell Scientific
dataloggers. This makes it simpler to program, and uses fewer measurement
channels.
Table 5-1 shows the thermistor resistance values as a function of temperature.
Relatively small errors occur when the CNR4 is not in thermal equilibrium.
This happens for example when the heater is on, or when the sun is shining.
When the heater and ventilator are on, the largest expected deviation between
the real sensor temperature and the thermistor reading is 1 degree. This results
in a worst case error for the pyrgeometer of 5 W/m2. When the sun is shining,
the largest expected deviation between the real sensor temperature and the
thermistor reading is again 1 degree. This results in a worst case error for the
pyrgeometer of 5 W/m2.
The thermistor will not give a good indication of ambient air temperature; at
1000 W/m2solar radiation, and no wind, the instrument temperature will rise
approximately 5 degrees above the ambient temperature.
The offsets of both the pyranometers and the pyrgeometers might be larger
than 5W/m2if large temperature gradients are forced on the instrument (larger
than 5 K/hr). This happens for example when rain hits the instrument. The
occurrence of this can be detected using the thermistor readout, and can be
used for data filtering.
10

CNR4 Net Radiometer
The thermistor measurement can be done by the datalogger, using the half
bridge measurement method which requires one voltage excitation and one
single-ended analog channel.
Alternatively, you can use the Pt-100 to make the temperature measurement.
In order to make the temperature measurement, using the Pt-100 sensor, you
will need one current excitation channel, and one differential analog channel.
Please refer to Appendix C for a sample program to measure Pt-100.
TABLE 5-1. Resistance values versus CNR4's thermistor temperature in °C.
Temperature
[°C]
Resistance
[Ω]
Temperature
[°C]
Resistance
[Ω]
Temperature
[°C]
Resistance
[Ω]
-30
-29
-28
-27
-26
-25
-24
-23
-22
-21
-20
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
135200
127900
121100
114600
108600
102900
97490
92430
87660
83160
78910
74910
71130
67570
64200
61020
58010
55170
52480
49940
47540
45270
43110
41070
39140
37310
35570
33930
32370
30890
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
29490
28150
26890
25690
24550
23460
22430
21450
20520
19630
18790
17980
17220
16490
15790
15130
14500
13900
13330
12790
12260
11770
11290
10840
10410
10000
9605
9227
8867
8523
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
8194
7880
7579
7291
7016
6752
6500
6258
6026
5805
5592
5389
5193
5006
4827
4655
4489
4331
4179
4033
3893
3758
3629
3504
3385
3270
3160
3054
2952
2854
11

CNR4 Net Radiometer
TABLE 5-2. Resistance values versus CNR4's Pt-100 temperature in °C.
Temperature
[°C]
Resistance
[Ω]
Temperature
[°C]
Resistance
[Ω]
Temperature
[°C]
Resistance
[Ω]
-30
-29
-28
-27
-26
-25
-24
-23
-22
-21
-20
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
88.22
88.62
89.01
89.40
89.80
90.19
90.59
90.98
91.37
91.77
92.16
92.55
92.95
93.34
93.73
94.12
94.52
94.91
95.30
95.69
96.09
96.48
96.87
97.26
97.65
98.04
98.44
98.83
99.22
99.61
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
100.00
100.39
100.78
101.17
101.56
101.95
102.34
102.73
103.12
103.51
103.90
104.29
104.68
105.07
105.46
105.85
106.24
106.63
107.02
107.40
107.79
108.18
108.57
108.96
109.35
109.73
110.12
110.51
110.90
111.28
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
111.67
112.06
112.45
112.83
113.22
113.61
113.99
114.38
114.77
115.15
115.54
115.93
116.31
116.70
117.08
117.47
117.85
118.24
118.62
119.01
119.40
119.78
120.16
120.55
120.93
121.32
121.70
122.09
122.47
122.86
5.4 Calculation of Albedo
Albedo is the ratio of reflected short-wave radiation to incoming short-wave
radiation. This unitless value ranges between 0 and 1. Typical values are 0.9
for snow, and 0.3 for grassland. To determine the albedo, the measured values
of the two pyranometers can be used. The pyrgeometers are not involved, as
they do not measure short-wave solar radiation. Do not use the measured
values when the solar elevation is lower than 10 degrees above the horizon.
Errors in the measurements at these elevations are likely and yield unreliable
results. This is due to deviations in the directional response of the
pyranometers.
Albedo = (E lower Pyranometer) / (E upper Pyranometer) (5-3)
12

CNR4 Net Radiometer
In the equation above, E is calculated according to the Equation 5-1.
Albedo will always be smaller than 1. Checking this can be used as a tool for
quality assurance of your data. If you know the approximate albedo at your
site, the calculation of albedo can also serve as a tool for quality control of your
measured data at a specific site.
5.5 Calculation of Net Short-wave Radiation
The net short-wave solar radiation is equal to the incoming (downwelling)
short-wave radiation minus the reflected (upwelling) short-wave radiation.
Net Short-wave Radiation = (E upper Pyranometer) - (E lower Pyranometer) (5-4)
In the equation above, E is calculated according to Equation 5-1.
Net short-wave solar radiation will always be positive. This can be used as a
tool for quality assurance of your measured data.
5.6 Calculation of Net Long-wave Radiation
The net long-wave far Infrared radiation is the part that contributes to heating
or cooling of the earth's surface. In practice, usually the net long-wave far
infrared radiation will be negative.
Net Long-wave Radiation = (E upper Pyrgeometer) - (E lower Pyrgeometer) (5-5)
In the equation above, E is calculated according to Equation 5-2. According to
equation 5-5 above, the terms that contain the sensor body temperature T
cancel each other. Therefore, if one is only interested in the net long-wave
radiation, instead of separate upper and lower components of the long-wave
radiation, the CNR4 temperature measurement is not required.
The E measured with the pyrgeometer actually represents the irradiance of the
sky (for upward- facing pyrgeometer) or the ground (for downward-facing
pyrgeometer). Assuming that these two, ground and sky, behave like perfect
blackbodies, theoretically, one can calculate an effective "Sky temperature"
and an effective "Ground temperature".
4/1
8
1067.5 ⎥
⎦
⎤
⎢
⎣
⎡
⋅
=−
rPyrgeometeupperE
atureSky temper
(5-6)
4/1
8
1067.5 ⎥
⎦
⎤
⎢
⎣
⎡
⋅
=−
rPyrgeometelowerE
eTemperaturGround
(5-7)
As a rule of thumb, for ambient temperatures of about 20 degrees Celsius, one
can say that one degree of temperature difference between two objects results
in a 5 W/m2exchange of radiative energy (infinite objects):
1 degree of temperature difference = 5 W/m2(rule of thumb)
13

CNR4 Net Radiometer
5.7 Calculation of Net (Total) Radiation
In the four separate components mode, net radiation, Rn, can be calculated
using the individual sensor measurement results:
R
n= {(E upper Pyranometer) - (E lower Pyranometer)}
+ {(E upper Pyrgeometer) - (E lower Pyrgeometer)} (5-8)
Where E upper/lower pyranometers are calculated according to Equation 5-1,
and E upper/lower pyrgeometers are calculated according to Equation 5-2. The
terms with T cancel each other out.
6. Wiring
The CNR4 has two outputs for short-wave radiation, two outputs for long-wave
radiation, thermistor output, and Pt-100 temperature sensor output. In addition,
if a user chooses to attach the optional CNF4 heater/ventilator unit, it will have
power wires for heater and ventilator. All wiring schemes shown in this
manual and the sample programs will use the thermistor for the temperature
measurement of the CNR4. The wiring diagrams for the thermistor in this
manual is applicable only if the CNR4 and the cables were purchased from
Campbell Scientific, Inc.
The CNR4 comes with two sets of cables labelled SOLAR and TEMP, as
shown in Figure 6-1. Figure 6-2 shows the marks by the connecting ports at
the sensor’s end for the cable connection: S and T for SOLAR and TEMP
cables, respectively. The two cables, SOLAR and TEMP, have identical
connectors, and care should be used to make sure that the correct cables are
connected to the correct ports of the sensor.
FIGURE 6-1. The CNR4 sensor with SOLAR and TEMP cables.
14